This invention relates to a mold for molding golf balls. More particularly, in connection with a golf ball comprising a core, an intermediate resin layer, and a cover, the invention relates to a mold defining therein a spherical cavity for molding the resin layer.
In the golf ball art, a number of attempts have been made for accomplishing improvements in both the distance and feel of golf balls. As to solid golf balls comprising a solid core and a cover, it is a common practice to form the core and the cover each to a multilayer structure and adjust the hardness and dimensions (e.g., diameter and gage) of the layers.
For example, U.S. Pat. No. 5,439,227 discloses a three-piece solid golf ball comprising a core, a cover inner layer and a cover outer layer wherein the cover outer layer is harder than the cover inner layer. U.S. Pat No. 5,490,674 discloses a three-piece golf ball comprising a solid core of inner and outer layers and a cover wherein the core inner layer is harder than the core outer layer.
Although the respective layers of such golf balls most often have a smooth spherical surface, there are known a few golf balls including an inside layer having a rugged surface. For the purpose of preventing the core from being off centered when the cover is injection molded over the core, it has been proposed to provide the core with radially outward extending projections. The core is placed in the spherical cavity of the mold before the cover is injection molded around the core. During the process, the projections on the core serve as support pins for holding the core at the center of the spherical cavity.
Referring to FIG. 10, there is illustrated a prior art mold 30 for molding a golf ball core having projections. The mold 30 defines a spherical cavity therein and includes at least a pair of upper and lower mold halves which are separable along the equator of the spherical cavity. Only the lower mold half 31 is illustrated in the figure. Each mold half has a cavity-defining surface 32 which is provided with dips 34. A suitable material is molded in the mold cavity to form a body 36. Since the molding material penetrates into the dips 34, the body 36 is formed on its surface with projections 38.
However, the projections 38 on the molded body 36 give rise to some problems. The projections 38 hinder removing the molded body 36 from the mold 30. Depending on the number, height and arrangement of projections, the removal of the molded body from the mold becomes difficult.
In connection with a golf ball of multilayer structure having a resin layer between a core and a cover, an object of the invention is to provide a mold defining a spherical cavity having projections for molding the resin layer, the mold having the advantage of ease of removal of the resin layer from the mold after molding and being free of substantial limits on the number and position of the projections. Another object of the invention is to provide a golf ball having the resin layer formed using the mold.
In connection with a golf ball comprising a core, a resin layer enclosing the core, and a cover enclosing the resin layer, the invention provides a mold defining therein a spherical cavity for molding the resin layer. The mold includes at least six segments which are removably assembled to define the spherical cavity. Each of the segments is provided on its cavity-defining surface with at least one projection.
Preferably, at least one of the projections on each segment has a height equal to the thickness of the resin layer and projects toward the center of the cavity. Typically, the projections have a height of 0.5 to 5.0 mm. More preferably, the projections have an axis and a cross section perpendicular to the axis, the cross section being circular and having a maximum diameter of 0.8 to 3.0 mm. Further preferably, the total number of projections on the entire segments is 6 to 500, and the projections are equidistantly spaced.
In one preferred embodiment, the mold includes a pair of mold halves which are removably mated along an equatorial plane of the spherical cavity. Each mold half is divided into at least three side segments each facing the equatorial plane. The mold may further include a mold half receptacle defining a hemispherical or frustoconical recess wherein each mold half having the side segments assembled together is received in the receptacle. The side segments are separately slidable on their outer surface along the receptacle recess so that the side segments may be removed from the receptacle.
In another aspect, the invention provides a golf ball comprising a core, a resin layer enclosing the core, and a cover enclosing the resin layer, the resin layer being molded using the mold defined above.
In the process of manufacturing a golf ball comprising a core, an intermediate resin layer, and a cover, the golf ball mold of the invention is intended to mold the resin layer around the core. Especially the golf ball which can be manufactured using the mold of the invention is of the unique structure that the resin layer is formed in its outer surface with a plurality of perforations, and the cover surrounding the resin layer protrudes into the perforations, so that the protrusions of the cover are engaged with the perforations in the resin layer.
According to the invention, the mold includes at least six segments which are removably assembled to define the spherical cavity, and each of the segments is provided on its cavity-defining surface with at least one projection. When a resin is molded in this mold, the resulting resin layer has in its outer surface with a plurality of perforations corresponding to the projections. When a cover material is molded around the resin layer, the cover material partially penetrates into the resin layer. Then the resin layer and the cover are intermixed or interdigitated at their interface to form a new layer having unique properties, enabling to impart a controlled profile of properties to the golf ball.
Since the mold is divided into at least six segments, the molded body can be removed from the mold simply by separating apart the segments although the projections are on the inner surface of the segments and have a substantial height.
The preferred embodiment wherein the projections on each segment has a height equal to the thickness of the resin layer and projects toward the center of the cavity has the advantage that when the core is held in the mold prior to forming the resin layer around the core, the core can be automatically and exactly centered because the projections play the role of support pins. This eliminates a need for core support means such as support pins which are needed in conventional molds for supporting the core in place. This, in turn, ensures effective molding.
In the further preferred embodiments wherein the mold includes a pair of mold halves, and each mold half is divided into at least three side segments, and wherein the mold half having the side segments assembled together is received in the receptacle, and the side segments are separately slidable along the receptacle recess, there are obtained advantages including easy separation of the segments and smooth removal of the molded body.